1. Field of Invention
The present invention relates generally to the field of middleware. More specifically, the present invention is related to middleware for query processing across a network of RFID databases.
2. Discussion of Prior Art
In recent years, Radio-Frequency Identification (RFID) has attracted a lot of attention. Although RFID technology is not new and can be traced back to World War II, a number of recent developments have accelerated the adoption of RFID technology in different industries.
Advancements in RFID physics and hardware technology have been pushing the average price of individual passive tags to be lower than ever. An initiative is underway in Japan to produce a 5 yen RFID tag by the end of 2006, 1.8 billion tags have been sold in 2005, and the total market opportunity for RFID has been predicted to reach seven billion dollars in 2008.
A number of legislations have pushed industries to consider RFID technology for compliance purposes. Recent laws passed in the US will require pharmaceutical industry to provide a valid pedigree of drug items upon request. Similar legislations have been formulated in the food industry, such as the Japanese Beef Traceability Law, the US Department of Agriculture national animal identification system, and the EU requirements on fish and fish products traceability.
Standardization efforts by industry consortia such as EPCglobal™ (formerly Auto-ID Center) have further promoted the adoption of RFID technology. EPCglobal™ is creating standards for RFID data communication such as a specification for RFID tag numbering formats, a transmission protocol to obtain information from RFID readers, and an overall architecture for a network of databases containing RFID data.
Recently several industry research papers have been published on RFID data management. SAP presented an overview on their existing RFID infrastructure in the paper titled “integrating Automatic Data Acquisition with Business Processes—Experiences with SAP's Auto-ID infrastructure”. Under “Lessons Learned”, they state that companies need to overcome their reluctance to collaborate because the full potential of RFID technology can only be unlocked through collaboration and data sharing across sites and organizations. ORACLE™ presented a new bitmap data type for ORACLE DBMS to support RFID-based item tracking applications in the paper titled “Supporting RFID-based Item Tracking Applications in ORACLE DBMS”. Siemens proposed a temporal data model for their RFID data management system in the paper titled “Temporal Management of RFID data.” OAT Systems™ gave a brief introduction to RFID technology, highlighting some of the data management challenges in the paper titled “Managing RFID Data”.
An RFID cube is introduced in the paper titled “Warehousing and Analyzing Massive RFID Data Sets” to support warehousing and analysis of massive RFID data sets. Apart from this work, academic research has mostly focused on privacy and security issues surrounding communication between RFID reader and RFID tag. An overview can be found in the paper titled “Radio Frequency Identification: Adversary Model and Attacks on Existing Protocols”. However, confidentiality of RFID data once it is stored in databases is not addressed. None of these papers presents solutions to the challenges imposed by independent organizations sharing data.
In the area of federated database systems, the issue of querying across heterogeneous data sources has been addressed, but those solutions rely on a priori knowledge about the data distribution (see paper to Kossmann titled “The State of the Art in Distributed Query Processing”). But with RFID traceability systems the distribution is unknown, since the tracked objects can move freely between organizations.
For peer-to-peer databases, work has been done on locating documents, which means to find the single place where all the information about an object is stored (see paper to Androutsellis-Theitokis et al. titled “A Survey of Peer-To-Peer Content Distribution Technologies” and the paper to Stoica et al. titled “A Scalable Peer-To-Peer Lookup Service for Internet Applications”). But in traceability systems the information about an entity is spread over several participating databases and the set of those databases may change at any point in time. Some ideas on collecting information about a single entity from several databases in a peer-to-peer setting have been presented in the paper to Giunchiglia et al. titled “Making Peer-to-Peer Databases Interact—A Vision for an Architecture Supporting Data Coordination”.
In the following, two existing industry solutions for implementing query processing in traceability networks are examined. The architectures differ in the amount of data-distribution supported. A central warehouse solution where every organization publishes its RFID data to a central site is first described. After that, a solution that is proposed by EPCglobal™ is described where each organization keeps RFID data in a local repository and only publishes data to central directory services (see paper to Chawathe et al. titled “Managing RFID Data” and paper to Traub et al. titled “The EPCglobal Architecture Framework”).
In the data warehouse approach, RFID data collected within each organization is published to a central data warehouse. In this case, all organizations have to agree on a common storage format for RFID data as well as for all property data they want to share with each other. Together with their data, each organization also has to publish its confidentiality or data sharing policy to the central data warehouse. Mechanisms such as web services are provided to organizations to query the stored data based on the policies installed, and query processing is performed entirely in the warehouse.
Since the heterogeneity aspects (e.g. data schema differences) do not exist in this approach, query processing is simplified as all data can be accessed in a uniform way. It becomes possible to do optimizations such as the RFID cube proposed in the paper to Gonzalez et al. titled “Warehousing and Analyzing Massive RFID Data Sets”, and incoming queries can he executed as-is against the database. However, as a query might span data from multiple owners there needs to be a way to detect and enforce multiple policies from different organizations. Additionally, as the amount of RFID data increases, the total amount of data that needs to be published may put serious constraints on such a central warehouse approach.
Rather than sending all data to a central warehouse, an alternative would be to allow data to be stored in local repositories at each organization and make those repositories accessible in the traceability network. The most notable proposal in this regard is the EPCglobal Framework (see paper to Chawathe et al. titled “Managing RFID Data” and paper to Traub et al. titled “The EPCglobal Architecture Framework”), which consists of a network with nodes (referred to as subscribers in EPCglobal Framework), and a number of central registries (called core services) that the nodes can utilize. Each node offers a simple, standardized query interface (called information service) to a repository with RFID data. An application (called accessing application) can use the standardized query interface of a repository in order to obtain data.
The challenge in such a network of distributed repositories is, given a traceability query, to locate the data sources that contain tuples that contribute to the answer construction. Central directory tables can be used to guide a query to the necessary nodes. The EPCglobal Framework proposes an Object Naming Service (ONS) and a Discovery Service (DS) as its core services. The Object Naming Service provides a centralized registry through which an object may be associated with the information service at the node where the object or more specifically its tag was created. An application may also use the Discovery Service to locate the information service of all EPCglobal subscribers that have information about, the object in question. This ensures that even if the other EPCglobal subscribers within a supply chain are not known to an application, it will be able to locate all information concerning a specific object.
All nodes have to update the core services with relevant information, for instance register with the Object Naming Service when a new RFID tag is created, or update the Discovery Service when a tag moves from one node to another.
Whatever the precise merits, features, and advantages of the above mentioned prior art techniques, none of them achieves or fulfills the purposes of the present invention.